In the prior art automobile transmission, a planetary gear or counter shaft type transmission mechanism has been utilized. It is a common practice to change the speed by engaging the separately installed clutch with the gear steps having different transmission ratios on a selective basis. This is a method for shifting the engine torque from the front position gear to the next position gear by changing the engagement of the friction clutch. Since friction loss occurs at the time of gear shift and the clutch is a passive device, torque transfer cannot be achieved in principle at the time of downshifting. This has been a problem in the prior art.
To solve this problem, the applicants of the present invention filed an application for an active transmission method for regenerating the energy discharged at the time of up-shifting, using a motor as an active device, and for pumping up the torque from the high-shift position of lower power to the low-shift position of higher power at the time of down-shifting as indicated by Japanese Patent Laid-Open No. 2002-204504.
Although the aforementioned active transmission system is capable of solving the problems of the transmission using a prior art clutch, it requires a large-capacity motor for gear shift. The required motor capacity is calculated by (transmission torque by motor speed). The maximum transmission torque is equal to the maximum engine torque. In a common transmission, the maximum motor speed is equal to the difference speed at the time of 1-2 shift; therefore, the motor capacity of 20 kW or more is required, for example, when a 1.5 L engine is used.
To permit gear shift with the smallest possible motor, the present applicant filed an application for a method for ensuring a 50-percent reduction of motor capacity by using an intermediate gear as indicated by Japanese Patent Laid-Open No. 2003-113934. Since this method does not require use of a clutch in the input shaft, it reduces both weight and cost.